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Exciton

About: Exciton is a research topic. Over the lifetime, 31603 publications have been published within this topic receiving 810642 citations.


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Journal ArticleDOI
TL;DR: An analytic expression for numerical simulations of time- and frequency-resolved 2D photon echo signals is obtained and it is found that there are two noncascading exciton energy relaxation pathways.
Abstract: A theoretical description of femtosecond two-dimensional electronic spectroscopy of multichromophoric systems is presented. Applying the stationary phase approximation to the calculation of photon echo spectra and taking into account exciton relaxation processes, we obtain an analytic expression for numerical simulations of time- and frequency-resolved 2D photon echo signals. The delocalization of one-exciton states, spatial overlaps between the probability densities of different excitonic states, and their influences on both one- and two-dimensional electronic spectra are studied. The nature of the off-diagonal cross-peaks and the time evolution of both diagonal and off-diagonal peak amplitudes are discussed in detail by comparing experimentally measured and theoretically simulated 2D spectra of the natural Fenna−Matthews−Olson (FMO) photosynthetic light-harvesting complex. We find that there are two noncascading exciton energy relaxation pathways.

436 citations

Journal ArticleDOI
TL;DR: This study reports a mechanism to electrically control second-order optical nonlinearities in monolayer WSe₂, an atomically thin semiconductor and paves the way towards a new platform for chip-scale, electrically tunable nonlinear optical devices based on two-dimensional semiconductors.
Abstract: Second-order optical nonlinearities can be controlled, up to room temperature, by electrostatic gating in a field-effect transistor made from atomically thin crystals of WSe2. Nonlinear optical frequency conversion, in which optical fields interact with a nonlinear medium to produce new field frequencies1, is ubiquitous in modern photonic systems. However, the nonlinear electric susceptibilities that give rise to such phenomena are often challenging to tune in a given material and, so far, dynamical control of optical nonlinearities remains confined to research laboratories as a spectroscopic tool2. Here, we report a mechanism to electrically control second-order optical nonlinearities in monolayer WSe2, an atomically thin semiconductor. We show that the intensity of second-harmonic generation at the A-exciton resonance is tunable by over an order of magnitude at low temperature and nearly a factor of four at room temperature through electrostatic doping in a field-effect transistor. Such tunability arises from the strong exciton charging effects in monolayer semiconductors3,4, which allow for exceptional control over the oscillator strengths at the exciton and trion resonances. The exciton-enhanced second-harmonic generation is counter-circularly polarized to the excitation laser due to the combination of the two-photon and one-photon valley selection rules5,6,7,8, which have opposite helicity in the monolayer. Our study paves the way towards a new platform for chip-scale, electrically tunable nonlinear optical devices based on two-dimensional semiconductors.

435 citations

Journal ArticleDOI
TL;DR: The chiral stationary phase for high-performance liquid chromatography shows good chiral recognition ability and can be synthesized by supramolecular chemistry techniques.
Abstract: Molecular aggregates are abundant in nature; they form spontaneously in concentrated solutions and on surfaces and can be synthesized by supramolecular chemistry techniques.1-3 Assemblies of chromophores play important roles in many biological processes such as light-harvesting and primary * To whom correspondence should be addressed. E-mail: smukamel@uci.edu. † University of California Irvine. ‡ Universität Würzburg. § Charles University. Chem. Rev. 2009, 109, 2350–2408 2350

434 citations

Journal ArticleDOI
TL;DR: This work investigates the conduction band valley structure in few-layer MX2 by examining the temperature-dependent shift of indirect exciton photoluminescence peak and identifies the origin of the indirect emission and concurrently determine the relative energy of these valleys.
Abstract: It has been well-established that single layer MX2 (M = Mo, W and X = S, Se) are direct gap semiconductors with band edges coinciding at the K point in contrast to their indirect gap multilayer counterparts. In few-layer MX2, there are two valleys along the Γ–K line with similar energy. There is little understanding on which of the two valleys forms the conduction band minimum (CBM) in this thickness regime. We investigate the conduction band valley structure in few-layer MX2 by examining the temperature-dependent shift of indirect exciton photoluminescence peak. Highly anisotropic thermal expansion of the lattice and the corresponding evolution of the band structure result in a distinct peak shift for indirect transitions involving the K and Λ (midpoint along Γ-K) valleys. We identify the origin of the indirect emission and concurrently determine the relative energy of these valleys.

434 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,269
20222,623
20211,045
20201,157
20191,096
20181,057